Segmentation (Jaccard).

For DAVIS2016, SegTrackv2 and FBMS59, pixelwise segmentation is provided;
thus we report the standard metric, region similarity (\(\mathcal {J}\) ),
computing the mean over the test set. For FBMS59 and SegTrackv2, we follow the common practice [1]}, [2]} and combine multiple objects as one single foreground.
